Interpenetrating network of anion-exchange polymers, production method thereof and use of same

ABSTRACT

The invention relates to a method for producing an anion-exchange polymer material having an IPN or semi-IPN structure, said method consisting in: (A) preparing a homogeneous reaction solution containing, in a suitable organic solvent, (a) at least one organic polymer bearing reactive halogen groups, (b) at least one tertiary diamine, (c) at least one monomer comprising an ethylenic unsaturation polymerizable by free radical polymerization, (d) optionally at least one cross-linking agent including at least two ethylenic unsaturations polymerizable by free radical polymerization, and e) at least one free radical polymerization initiator; and (B) heating the prepared solution to a temperature and for a duration that are sufficient to allow both a nucleophilic substitution reaction between components (a) and (b) and a free radical copolymerization reaction of components (c) and optionally (d) initiated by component (e). The invention also relates to the resulting IPN or semi-IPN material and to the use thereof in electrochemical devices, in direct contact with an air electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/318,497, filed Nov. 2, 2011, which is a National Stage ofPCT/FR2010/050846 filed May 4, 2010, which claims priority benefit ofFrench Patent Application No. FR 09 53021 filed May 6, 2009. The entirecontent of each of the aforementioned applications is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method for producing ananion-exchange polymer material having an interpenetrating polymernetwork (IPN) or semi-interpenetrating polymer network (semi-IPN)structure, to the polymer material obtained by means of this method andto the use thereof in electrochemical devices, in contact with an airelectrode.

BACKGROUND OF THE INVENTION

For decades, many studies have been carried out in order to develop andoptimize air electrodes that make it possible to produce electrochemicalgenerators of metal-air type, which are known for their high energies byweight, that can reach several hundred Wh/kg.

Air electrodes are also used in alkaline fuel cells which areparticularly advantageous compared with other systems owing to the highreaction kinetics at the electrodes.

An air electrode makes it possible to use, as oxidizing agent for theelectrochemical reaction, air from the atmosphere, which is available inunlimited amount anywhere and at any time.

An air electrode is a porous solid structure in contact with the liquidelectrolyte, which is generally an alkaline solution. The interfacebetween the air electrode and the liquid electrolyte is a “triplecontact” interface where the active solid material of the electrode, theoxidizing gas (air) and the liquid electrolyte are simultaneouslypresent. This triple contact interface has always posed numerousdifficulties linked in particular to the gradual degradation, even whennot operating, of the air electrode, in particular when the liquidelectrolyte is a concentrated alkaline solution, such as a several timesmolar solution of sodium hydroxide, potassium hydroxide or lithiumhydroxide.

The drawbacks of air electrodes in alkaline fuel cells are set out, forexample, in the literature article by G. F. McLean et al., entitled “Anassessment of alkaline fuel cell technology”, International Journal ofHydrogen Energy 27 (2002), 507-526:

-   -   these electrodes undergo gradual wetting of their porous        structures until flooding thereof which makes them ineffective.        This change is accelerated during operation of the fuel cell or        of the battery;    -   in the long term, the carbon dioxide present in the air diffuses        toward and dissolves in the alkaline solution forming the        electrolyte, in the form of a carbonate anion which precipitates        in the presence of alkaline cations (Na, K, Li). A gradual and        inevitable carbonation of the electrolyte is thus observed;    -   carbonates form mainly at the liquid/porous solid interface and        promote the flooding phenomenon mentioned above;    -   the carbonate precipitation gradually destroys the structure of        the air electrode and considerably reduces the charge transfer        kinetics at the triple point, which ends up making the electrode        ineffective.

The objective of the present invention was to develop anion-conductingcationic polymer materials capable of being interposed between the airelectrode and the liquid alkaline electrolyte or else of replacing thelatter, in order to substantially reduce, or even eliminate, thecarbonation of the solid electrolyte and the degradation of the airelectrode which results therefrom.

Such materials should be usable in alkaline fuel cells and metal-airbatteries, either as a solid electrolyte, or as membrane separating theair electrode from the alkaline liquid electrolyte.

The applicant has proposed, in international application WO 2006/016068,a crosslinked organic polymer material, in particular asanion-conducting solid electrolyte in alkaline fuel cells. The polymermaterial described in this application is obtained by a nucleophilicsubstitution between a halogenated linear polymer, such aspolyepichlorohydrin, and a combination of at least one tertiary diamineand of at least one tertiary or secondary monoamine. The reactionbetween the tertiary amine functions and the chlorinated functions ofthe polymer results in the formation of quaternary ammonium functionsresponsible for the anion-conducting power of the polymer materialobtained. Moreover, the reaction of the two tertiary amine functions ofthe bifunctional reactant (tertiary diamine) results in the crosslinkingof the polymer and in the formation of an insoluble three-dimensionalnetwork.

However, this crosslinked anion-conducting material based onpolyepichlorohydrin comprising quaternary ammonium groups is not stablein concentrated alkaline solutions. Moreover, it is not self-supportedand, in order to obtain it in the form of a large membrane that can behandled, it is necessary to synthesize it on a support or in a porous orfibrous structure, for example a nonwoven textile made of polypropylene.

The applicant, in the context of its research aimed at developingimproved anion-conducting organic materials capable of being used infuel cells or batteries in order to reduce the degradation of airelectrodes, has discovered that it is possible to overcome the drawbacksdescribed above, by incorporating a polymeric system as described in WO2006/016068 into an interpenetrating polymer network (IPN) or asemi-interpenetrating polymer network (semi-IPN).

An interpenetrating polymer network (IPN) is a polymeric systemcomprising at least two networks of polymers of which at least one hasbeen synthesized in the presence of the other, without, however, beinglinked to one another by covalent bonds, and which cannot be separatedfrom one another without breaking chemical bonds (IUPAC Compendium ofChemical Terminology, 2nd edition, 1997).

A semi-interpenetrating polymer network (semi-IPN) differs from an IPNby virtue of the fact that one of the at least two polymers present doesnot form a three-dimensional network, i.e., is not crosslinked, but is alinear or branched polymer. Owing to the absence of crosslinking of thesecond polymeric system, the latter can be separated from the first byextraction.

SUMMARY OF THE INVENTION

Consequently, a subject of the present invention is a method forproducing an anion-exchange polymer material having an interpenetratingpolymer network (IPN) or semi-interpenetrating polymer network(semi-IPN) structure, said method comprising the following successivesteps:

-   -   (A) preparing a homogeneous reaction solution comprising, in a        suitable organic solvent,        -   (a) at least one organic polymer bearing reactive            halogenated groups,        -   (b) at least one tertiary diamine,        -   (c) at least one monomer comprising an ethylenic            unsaturation polymerizable by free-radical polymerization,            and        -   (d) optionally, at least one crosslinking agent comprising            at least two ethylenic unsaturations polymerizable by            free-radical polymerization, and        -   (e) at least one free-radical polymerization initiator,    -   (B) heating the solution prepared in step (A) to a temperature        and for a duration that are sufficient to allow both a        nucleophilic substitution reaction between components (a)        and (b) and a free-radical copolymerization reaction of        components (c) and optionally (d), initiated by component (e).

The method of the present invention thus comprises the simultaneouscarrying out of two reactions which do not interfere with one another:

-   -   a nucleophilic substitution reaction between the halogenated        organic polymer and the tertiary diamine, resulting in the        formation of an insoluble, crosslinked, three-dimensional        polymer network bearing quaternary ammonium groups, and    -   a free-radical polymerization reaction of the monomers and        optionally of the crosslinking agent, initiated by the        free-radical initiator, and which results in the formation of a        second polymer network intermingled with the first. When the        system contains a sufficient amount of a crosslinking agent (d),        this second polymer network is three-dimensional, crosslinked        and insoluble.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the degree of swelling in water as afunction of time.

FIG. 2 is a graph representing the anionic conductivity in water,expressed as S/cm, of the membranes of examples 1 and 2 as a function ofthe percentage of crosslinked PECH.

FIG. 3 shows the polarization curves obtained for a cell containing asolution of LiOH at 2 mol·L⁻¹ with an Hg/HgO reference electrode and astainless steel counter electrode.

FIG. 4 illustrates the change in polarization during discharge of airelectrodes.

FIG. 5 illustrates the change in storage moduli of the IPN membrane andof the corresponding simple networks.

FIG. 6 illustrates the corresponding loss modulus/storage modulus as afunction of temperature.

DETAILED DESCRIPTION

In one preferred embodiment of the invention, the reaction mixturecontains a crosslinking agent (d) and the polymer network formed is anIPN and not a semi-IPN.

The halogenated organic polymer can be chosen from all homopolymers andcopolymers comprising halogenated functions which are reactive withrespect to the tertiary amine functions of the diamine. The halogenatedfunctions are preferably chlorinated or brominated groups, in particularC₁₋₆ chloroalkyl or C₁₋₆ bromoalkyl groups.

Moreover, the organic polymer bearing reactive halogenated groups ispreferably chosen from homopolymers and copolymers with a polyetherbackbone. By way of examples of polymers that are particularlypreferred, mention may be made of epichlorohydrin homopolymers andepichlorohydrin/ethylene oxide copolymers.

By way of example of a tertiary diamine (component (b)), mention may bemade of tetramethylenediamine, 1,4-diazobicyclo[2,2,2]octane (DABCO),N-methylimidazole, bipyridine, diimidazoline and mixtures thereof. Thetertiary diamine serves both to crosslink the halogenated organicpolymer and to introduce positive charges essential for the anionicconduction of the polymer material prepared. Indeed, each tertiary aminefunction will be converted, after reaction with a chlorinated function,to a quaternary ammonium. Although the method claimed envisionsexplicitly the reaction between the halogenated polymer and a tertiarydiamine, it also encompasses a variant wherein the halogenated polymerhas been premodified by attachment of the diamine, leaving the secondamine function free for a subsequent crosslinking reaction.

The presence of the tertiary diamine is essential for the formation of acrosslinked three-dimensional network. In order to obtain a satisfactorydegree of crosslinking, the diamine/halogenated organic groups molarratio is generally between 1 and 80%, preferably between 2 and 40% andin particular between 10 and 30%.

It may be useful to introduce into the starting reaction solution (A),in addition to the tertiary diamine essential for crosslinking, atertiary monoamine (component b′)). The reaction of the latter with thehalogenated organic polymer makes it possible to increase the chargedensity of the cationic network and therefore its anionic conductivity,without however modifying the crosslinking density.

By way of examples of tertiary monoamines that can be used in thepresent invention, mention may be made of triethanolamine, quinuclidine,quinuclidinol and mixtures thereof.

Component (c) of the reaction mixture prepared in step (A) can inprinciple be any monoethylenic monomer polymerizable by free-radicalpolymerization, provided that it does not interfere with thenucleophilic substitution reaction of components (a) and (b). Thus,monochlorinated or polychlorinated vinyl monomers, such as vinylchloride or vinylidene chloride, are unsuitable as component (c) sincethey could participate in a nucleophilic substitution reaction with thetertiary diamine and thus result in the formation of covalent bondsbetween the two IPN or semi-IPN networks.

The monomers (c) are preferably uncharged or bear a cationic charge. Theuse of comonomers bearing an anionic charge (such as (meth)acrylic acidor styrenesulfonate) will in fact probably disrupt the ionic conductionbehavior of the final material obtained and is consequently advisedagainst.

By way of examples of monomers that can be used as component (c),mention may be made of the following monomers:

-   -   C1-10 Alkyl acrylates and methacrylates, C1-10 hydroxyalkyl        acrylates and methacrylates, styrene and its derivatives,        polyethylene glycol acrylates and methacrylates, vinyl acetate,        N-vinylpyrrolidone, acrylonitrile, (vinylbenzyl) tri (C1-6        alkyl) ammonium chloride or bromide, tri (C1-6 alkyl)        vinyloxycarbonyl-alkylammonium chloride or bromide, and        allyloxy-carbonyl (C1-6 alkyl) tri (C1-6 alkyl) ammonium        chloride or bromide.

Among these, C₁₋₄ alkyl methacrylates, polyethylene glycolmethacrylates, C₁₋₄ hydroxyalkyl methacrylates and vinyl acetate areparticularly preferred.

The crosslinking agent (component (d)) comprising at least two ethylenicunsaturations is optional in the case of a semi-IPN, but necessarilypresent when it is desired to prepare an IPN. It is chosen, for example,from the group made up of divinylbenzene, ethylene glycoldi(meth)acrylate, poly(ethylene oxide) glycol di(meth)acrylate andbisphenol A di(meth)acrylate. The notation “(meth)acrylate” used hereinencompasses acrylates, methacrylates and combinations of both.

When it is present, the crosslinking agent is preferably used in aproportion of from 0.5 to 10% by weight, preferably 0.5 to 5% by weight,relative to the monounsaturated ethylenic monomer (component (c)).

In one variant of the method of the invention, the polymerizable monomer(component (c))+crosslinking agent (component (d)) system can bereplaced with a component, subsequently referred to as component (cd),which plays the role of components (c) and (d). Said component (cd) is apolymer, preferably having a number-average molecular weight of between300 and 4000, comprising, preferably at each of its ends, a double bondpolymerizable by free-radical polymerization. When such a polymercomprising polymerizable double bonds is placed in the presence of afree-radical initiator, the double bonds polymerize and result in thecrosslinking of the polymer and in the formation of a three-dimensionalnetwork. The more or less loose nature of this network depends on themolecular weight of the polymer. The higher said molecular weight, theless crosslinked the network obtained will be.

A subject of the present invention is consequently also a method asdescribed above, in which components (c) and (d), in step (A), arereplaced with or combined with an organic polymer comprising at leasttwo groups comprising a polymerizable double bond (component (cd)),preferably located at the end of the organic polymer.

By way of example of such a component (cd), mention may be made ofpolyethylene glycol dimethacrylate.

Any compound capable of decomposing under the effect of heat and/or oflight, to give free radicals that are sufficiently stable to initiatethe polymerization reaction, can in principle be used as initiator(component (e)). Such initiators are known by those skilled in the art.Thermal initiators such as peroxides, diazo compounds or persulfateswill preferably be used. By way of example of such thermal initiators,mention may be made of ammonium persulfate, hydrogen peroxide, benzoylperoxide (BPO), azobisisobutyronitrile (AIBN) and dicyclohexylperoxycarbonate (DHPC).

Among the latter, BPO and AIBN are particularly suitable at thetemperatures used.

When the initiator is a photoinitiator, the polymerization is carriedout under radiation of suitable wavelength and intensity.

The initiator is preferably used in an amount of between 0.1 and 10% byweight, preferably between 1 and 5% by weight, relative to the totalweight of components (c) and (d).

By way of example of an organic solvent suitable for preparing theinitial reaction solution containing components (a)-(e), mention may bemade of dimethylformamide, ethanol, dimethyl sulfoxide, methanol,acetone, butanol, butanone or a mixture of these solvents.

In order to obtain, at the end of step (B), polymer materials having asuitable consistency, the initial reaction solution preferably has anoverall concentration of components (a)-(e) of between 10 and 80% byweight; in other words, the proportion of the organic solvent in theinitial solution is preferably between 90 and 20% by weight.

The weight ratio of components (a) and (b), including (b′), forming thefirst three-dimensional network bearing cationic charges, to components(c)-(e) forming the second three-dimensional network, which ispreferably uncharged, can vary between very broad limits, on thecondition that the final material has a conductivity which is sufficientfor the envisioned application.

Generally, the weight ratio of the components forming the cationic firstpolymer network, to the components forming the second polymer network,is between 90/10 and 10/90, preferably between 80/20 and 15/85, and inparticular between 60/40 and 25/75.

During step (B) of the method of the invention, the homogeneous reactionsolution containing all of the reactants (a)-(e), including optionallythe monofunctional amine (component b′), is heated to a temperaturesufficient to trigger both the nucleophilic substitution reactionbetween components (a) and (b) and (b′) optionally present, and thedecomposition of the polymerization initiator. The two reactions thuspreferably take place in parallel and simultaneously and result in theformation of an IPN or semi-IPN material having a uniform composition,consisting respectively of two mutually interpenetrating polymernetworks or of a linear or branched polymer entangled within acrosslinked polymer network.

In one variant, it is possible to envision a system which reacts in twosteps, the formation of one of the two networks being activated at atemperature below the temperature of activation of the other polymernetwork.

The heating temperature of step (B) is preferably between 30 and 130°C., in particular between 35 and 100° C. and even more preferentiallybetween 50 and 80° C. This temperature is generally maintained for aduration of between 1 and 24 hours, preferably of between 6 and 16hours.

As explained in the introduction, the IPN or semi-IPN polymer materialobtained at the end of the method according to the invention can be usedin an alkaline fuel cell or in a metal-air battery or cell in directcontact with an air electrode, either as a solid electrolyte replacingthe liquid alkaline electrolyte, or as an anion-conducting solidseparation membrane, inserted between the air electrode and the liquidelectrolyte.

In applications where it is important to provide very good adhesion ofthe IPN or semi-IPN material of the present invention to the airelectrode, it may be advantageous to carry out step (B) in the presenceof the air electrode. For this, the solution prepared in step (A) ispoured as a thin layer over the air electrode so as to preferablycompletely cover the surface containing the active material thereof, andthe whole is subjected to heating step (B). In this embodiment, thesolution can penetrate, to a small depth (generally at most equal to 5%of the total thickness of the electrode), into the porous structure ofthe electrode and polymerize/crosslink in situ, thus establishing astrong bond between the final crosslinked polymer material and theelectrode.

Such a composite air electrode, made up of a known air electrode and ananion-conducting IPN or semi-IPN material polymerized in situ at thesurface of the air electrode, is also a subject of the presentinvention. This composite electrode is characterized in that the IPN orsemi-IPN material extends into a part of the porous network of the airelectrode, penetrating this porous network to a depth at most equal to5%, preferably at most equal to 2% of the total depth of the airelectrode.

However, it is also possible to carry out step (B) in the absence of theair electrode, for example by maintaining the solution being twononporous support plates or by casting followed by evaporation. Theapplicant has noted that the fine membrane obtained at the end of step(B) can then be handled without problems and be stuck directly andeasily onto the air electrode, without the use of an adhesive (i.e.,without a membrane solution), by simply applying pressure.

To the knowledge of the applicant, the material obtained at the end ofthe method described above has up until now never been synthesized orproposed as an anion-conducting membrane or solid electrolyte inelectrochemical devices. Consequently, a subject of the presentinvention is also an anion-exchange polymer material having aninterpenetrating polymer network (IPN) or semi-interpenetrating polymernetwork (semi-IPN) structure that can be obtained by means of the methodas described above.

This material preferably has a charge density of from 0.3 to 2 meq pergram.

Its intrinsic ionic conductivity is preferably greater than 10⁻⁶ S·cm⁻¹,generally between 10⁻⁶ S·cm⁻¹ and 10⁻⁶ S·cm⁻¹, and in particular between10⁻⁴ S·cm⁻¹ and 5×10⁻³ S·cm⁻¹.

It is a relatively hydrophilic material which swells when it is broughtinto contact with water. The degree of swelling of the material of thepresent invention is, however, considerably lower than the degree ofswelling of a crosslinked polymer material of the prior art, preparedfrom components (a) and (b/b′) only (see example 3 hereinafter). Thedegree of swelling of the polymer material of the present invention, asdefined in example 3 of the present application, is preferably between10 and 40%, in particular between 12 and 30%.

A subject of the present invention is also the use of an anion-exchangeIPN or semi-IPN material as described above, as a solid electrolyte inan electrochemical device.

As indicated in the introduction, the anion-exchange IPN material of thepresent invention is particularly useful in alkaline fuel cells (AFCs)using porous air electrodes in contact with the alkaline electrolyte.

In such a fuel cell, the IPN or semi-IPN material of the presentinvention can either replace the alkaline liquid electrolyte or it canbe placed at the air electrode/liquid alkaline electrolyte interface. Inthe latter case, it effectively prevent or reduces the diffusion of thecarbon dioxide contained in the air to the liquid electrolyte and thecarbonation thereof. It also reduces, or even eliminates, the risk offlooding of the porous structure of the air electrode by the liquidelectrolyte. The lifetime of a fuel cell containing, in place of theliquid electrolyte or in combination therewith, an anion-conducting IPNor semi-IPN material in direct contact with the air electrode is thusconsiderably increased.

In another embodiment of the present invention, the IPN or semi-IPNmaterial is used in an air-metal cell or battery, in direct contact withthe air electrode, in the form of a membrane separating the airelectrode from the liquid electrolyte.

It is also possible to envision the use of the IPN or semi-IPN materialof the present invention as a replacement for the liquid electrolyte inany alkaline battery, such as NiMH or NiOOH—Zn, NiOOH—Cd, AgO—Zn, etc.

Example 1 Preparation of an IPN Material Based on CrosslinkedPolyepichlorohydrin and on Crosslinked Poly(Hydroxyethyl Methacrylate)

An ethanolic solution containing 200 g/L of an epichlorohydrin polymer(PECH) grafted beforehand with 12% by weight of1,4-diazabicyclo[2,2,2]octane (DABCO) is prepared. 0.9 g of hydroxyethylmethacrylate (HEMA), 0.1 g of ethylene glycol dimethacrylate(crosslinking agent) and 0.05 g of azobisisobutyronitrile (AIBN,free-radical initiator) are dissolved in 4 ml of this solution. Thesolution is degassed under a stream of argon and with stirring for 30minutes at ambient temperature. The solution is then placed in a moldmade up of two glass plates (5 cm×5 cm) separated by a Teflon® seal 1 mmthick. The filled mold is placed in an oven at 60° C. for 16 hours. TheIPN membrane obtained after demolding is homogeneous and transparent andhas a consistency which allows it to be handled easily.

In the membrane, the weight ratio of the first polymer network(crosslinked PECH) to the second polymer network (crosslinked PHEMA) is44/56 (=PECH content of 44%).

Example 2

IPN membranes are prepared, in the manner described in example 1, byvarying the initial proportions of the reactants so as to obtain PECHcontents of 10%, 22%, 30% and 37.5% by weight, as are two controlmembranes containing, respectively, 0% of crosslinked PECH (i.e.,containing 100% of poly(hydroxyethyl methacrylate) crosslinked withdiethylene glycol dimethacrylate, PHEMA-EGDMA) and 100% of PECHcrosslinked with DABCO.

Example 3 Determination of the Degree of Swelling in Water of theMembranes as a Function of Immersion Time-Anionic Conductivity

The membranes prepared in example 2, containing respectively 0%, 10%,22%, 37.5% and 100% of crosslinked PECH, are immersed in distilled waterat 23° C.

At regular intervals, the membrane is removed from the water in order todetermine its weight.

The degree of swelling is calculated according to the formulaD _(s)=(W _(t) −W ₀)/W ₀

The various curves of degree of swelling in water as a function of timeare represented in FIG. 1.

It is observed that the degree of swelling in water of the 100%crosslinked PECH control membrane is approximately 75% after about tenminutes, whereas that of all the other membranes is less than 30%. Theswelling in water of the 100% crosslinked PECH membrane results inmechanical weakening of the membrane. The membrane cannot be handled andis unusable.

The IPN membranes containing 10%, 22% and 37.5% of PECH and thePHEMA-EGDMA membrane retain their good dimensional and mechanicalproperties. Their moderate degree of swelling, of about 20 to 25% byweight, provides a suitable amount of water for good anionic conduction.

FIG. 2 represents the anionic conductivity in water, expressed as S/cm,of the membranes of examples 1 and 2 as a function of the percentage ofcrosslinked PECH. This figure shows that a crosslinked PECH content ofless than 20% by weight confers insufficient anionic conductivity on theIPN membrane. However, this threshold can be expected to be all thelower, the higher the DABCO/PECH ratio.

Example 4 Production of a Composite Air Electrode by In SituPolymerization and by Separate Polymerization

A membrane having a thickness of 100μ, prepared in the manner describedin example 1, is manually applied to the surface of an air electrodelocated on the side of the electrolyte. It is noted that the membraneadheres perfectly to the surface of the electrode (composite electrodeA).

A degassed homogeneous reaction solution prepared in the mannerdescribed in example 1 is deposited at the surface of an identical airelectrode. The whole is placed in a thermostated oven at 60° C. for 12hours. A composite air electrode bearing, at its surface, a deposit ofIPN material having a thickness of about 60μ is obtained (compositeelectrode B).

Example 5

The two composite air electrodes of example 4 are each mounted in a cellcontaining a solution of LiOH at mol·L⁻¹, with an Hg/HgO referenceelectrode and a stainless steel counter electrode for theelectro-chemical tests.

FIG. 3 shows the polarization curves obtained for such a cell. The curve(a) corresponds to a cell with a nonmodified air electrode, the curve(b) to a cell with a composite electrode B (example 4), the curve (c) toa cell with a composite electrode A (example 4) and the curve (d) to acell with an electrode covered with a commercial membrane based on anetwork (non-IPN) of crosslinked PECH incorporated into an inert porousstructure made of polypropylene (membrane sold by the company ERASLABO).

It is noted that the polarization of the air electrode modified with thecommercial membrane is very high and exceeds −1V for a current densityof only −10 mA·cm⁻². The use of such a membrane under the conditionsdescribed above, i.e., brought directly into contact with the airelectrode in the absence of a membrane solution, is thereforeimpossible. Conversely, the polarizations noted for the composite airelectrodes according to the present invention (curves (b) and (c)) areadvantageously almost identical to that of the naked air electrode. Theaddition of these membranes to the electrode does not therefore induceany significant drop in potential in the device at these currentdensities The ionic contact between the IPN membranes and the airelectrode is satisfactory in the absence of any membrane solution.

Example 6 Stability of the Air Electrodes in an Alkaline Medium

Electrochemical test devices are prepared with

-   -   (i) a nonmodified (naked) air electrode;    -   (ii) an air electrode according to the invention modified with        an IPN (composite electrode A of example 4);    -   (iii) a comparative air electrode, modified with a 100%        PECH-DABCO membrane.

The 100% PECH-DABCO membrane (thickness 100μ) is prepared by heating asolution of PECH-DABCO (100 g/L in an ethanol/butanone mixture (80/20))for 12 hours at 60° C.

The polarization measurements are carried out relative to an Hg/HgOelectrode with a current density of −10 mA·cm⁻². Before the beginning ofthe discharge, the modified electrodes are equilibrated for 2 hours inthe electrochemical cell previously described containing LiOH at 2mol·L⁻¹.

FIG. 4 shows the change in polarization during discharge of the airelectrodes (i), (ii) and (iii) described above.

The air electrode (ii) according to the invention resists for more than100 hours during discharge in lithium hydroxide, whereas the lifetime ofthe two comparative electrodes (i) and (iii) does not exceed 20 to 30hours.

Similar results are obtained with a saturated solution of lithiumhydroxide.

Example 7 Synthesis of an IPN Membrane According to the InventionCombining a Crosslinked PECH Network and a Network Based on a Component(Cd)

0.95 g of polyethylene glycol dimethacrylate (PEGDMA, Mn=750 g/mol⁻¹)and 0.047 g of AIBN are dissolved in 4 ml of a solution ofpolyepichlorohydrin modified with 12% of DABCO (100 g/L⁻¹). The solutionis degassed under a stream of argon and with stirring for 30 minutes atambient temperature. The solution is then placed in a mold made up oftwo glass plates (5 cm×5 cm) separated by a Teflon® seal 1 mm thick. Thefilled mold is placed in an oven at 60° C. for 16 hours. The IPNmembrane obtained after molding is homogeneous and transparent and canbe easily handled.

The PEGDMA/crosslinked PECH weight ratio of the IPN material is 71/29.

The results of the dynamic thermomechanical analysis of the resultingIPN material are represented

-   -   in FIG. 5, which shows the change in storage moduli of the IPN        membrane and of the corresponding simple networks (synthesized        separately), and    -   in FIG. 6, which gives the corresponding tan δ curves (tan        δ=loss modulus/storage modulus) as a function of temperature.

A single mechanical relaxation is observed for the IPN membrane. Themodulus of the rubbery plateau in the IPN (1.5 MPa) is very close tothat of the simple crosslinked PECH network (0.6 MPa). Thus, the PECHnetwork forms a continuous phase in the IPN membrane, which is inagreement with the quite high value of the anionic conductivity,measured for this membrane as being equal to 10⁻³ S·cm⁻¹ at ambienttemperature.

It can be deduced from the thermomechanical analysis results that thePEGDMA and PECH networks interpenetrate correctly, since the curve oftan δ as a function of temperature exhibits a single mechanicalrelaxation, characterized by a single intermediate peak positionedbetween the two peaks observed for each of the corresponding simplenetworks.

Example 8

A series of IPN networks based on crosslinked PECH and on polyethyleneglycol dimethacrylate (PEGDMA−Mn=750 g·mol⁻¹) is prepared, in the mannerdescribed in example 7, by varying the crosslinked PECH content from 10to 29% by weight (=90 to 71% of PEGDMA).

All these membranes have a satisfactory mechanical strength which makesit possible to handle them easily, and it is possible to position themon the electrode according to example 4 (composite electrode A).However, this assembly exhibits a very high polarization. In order todecrease this polarization, it is necessary to use a membrane solutionplaced between the electrode and the IPN membrane. A study of thestability of composite electrode A thus prepared, similar to thatdescribed in example 6, shows that this composite electrode A has astability curve identical to that of an electrode modified with a 100%PECH-DABCO membrane ((iii) in example 6).

Example 9 Influence of the Molecular Weight of the Component (Cd)

IPN membranes are prepared, in the manner described in example 8, using,in place of the PEGDMA of M_(n) equal to 750 g·mol⁻¹, a PEGDMA of M_(n)equal to 330 g·mol⁻¹ and to 550 g·mol⁻¹. The decrease in molar mass ofthe PEGDMA makes it possible to increase the density of crosslinking ofthe corresponding network. The membranes are then more rigid and theirdegree of swelling in lithium hydroxide decreases. However, thesemodifications did not make it possible to increase the lifetime of acomposite electrode A containing such a membrane.

The invention claimed is:
 1. An anion-exchange polymer material havingan interpenetrating polymer network (IPN) or semi-interpenetratingpolymer network (semi-IPN), wherein the IPN or semi-IPN comprises: afirst polymer network that is a three-dimensional polymer networkbearing quaternary ammonium groups; wherein the first polymer network isan epichlorohydrin polymer grafted with 1,4-diazabicyclo[2,2,2]octaneand a second polymer network intermingled with the first polymernetwork; wherein said anion-exchange polymer material having IPN, with adegree of swelling of between 10 and 40% and a charge density of from0.3 to 2 meq per gram.
 2. The anion-exchange polymer material of claim1, wherein the second polymer is obtained from a monomer chosen form thegroup consisting of C₁₋₁₀ Alkyl acrylates and methacrylates, C₁₋₁₀hydroxyalkyl acrylates and methacrylates, styrene and its derivatives,polyethylene glycol acrylates and methacrylates, vinyl acetate, Nvinylpyrrolidone, acrylonitrile, (vinylbenzyl)tri(C1-6-alkyl)ammoniumchloride or bromide, tri(C₁₋₆-alkyl)vinyloxycarbonyl-alkylammoniumchloride or bromide, andallyloxy-carbonyl(C₁₋₆-alkyl)tri(C₁₋₆-alkyl)ammonium chloride orbromide.
 3. The anion-exchange polymer material of claim 1 or claim 2,wherein the weight ratio of the first polymer network to the secondpolymer network is between 90/10 and 10/90.
 4. The anion-exchangepolymer material of claim 1 or claim 2, having an intrinsic ionicconductivity greater than 10⁻⁶ S·cm⁻¹.
 5. The anion-exchange polymermaterial of claim 1 or claim 2, having a degree of swelling of between12 and 30%.
 6. The anion-exchange polymer material of claim 1 or claim2, wherein the second polymer network is a poly(hydroxyethylmethacrylate).
 7. A composite air electrode comprising an air electrodepresenting a porous network and the anion-exchange polymer material ofclaim 1 or claim
 2. 8. The composite air electrode of claim 7, whereinthe IPN or semi-IPN material penetrates the porous network of the airelectrode to a depth at most equal to 5%, preferably at most equal to 2%of the total depth of the air electrode.
 9. An alkaline fuel cell,comprising a cathode, an anode and a solid electrolyte placed betweenthe anode and the cathode, wherein the solid electrolyte is theanion-exchange polymer material of claim 1 or claim
 2. 10. The alkalinefuel cell of claim 9, wherein the cathode is an air electrode.
 11. Anair-metal cell or battery containing an air electrode, a secondelectrode of opposite polarity to the air electrode and a liquidelectrolyte based on a concentrated aqueous solution of alkali metalhydroxide, wherein the anion-exchange polymer material of claim 1 orclaim 2 covers the air electrode over at least a part of its surface,preferably over its entire surface, in contact with the liquidelectrolyte.
 12. The anion-exchange polymer material of claim 3, whereinthe weight ratio of the first polymer network to the second polymernetwork is between 80/20 and 15/85.
 13. The anion-exchange polymermaterial of claim 3, wherein the weight ratio of the first polymernetwork to the second polymer network is between 60/40 and 25/75. 14.The anion-exchange polymer material of claim 4, having an intrinsicionic conductivity generally between 10⁻⁶ S·cm¹ and 10⁻² S·cm⁻¹.
 15. Theanion-exchange polymer material of claim 4, having an intrinsic ionicconductivity between 10⁻⁴ S·cm⁻¹ and 5×10⁻³ S·cm⁻¹.